The largest size Nylabone is the safest toy made. Kongs are tough but they have to be watched because a real determined chewer can get pieces off. The Jolly teaser ball is good, too but like the kong has to be checked regularly to make sure the dogs aren't chewing it. Dr. foster sell a hard plastic ball that can't be chewed or punctured. That's all I know of that I would trust my boys with!